FIG. 6 is a view showing the configuration of a test system 100 of an engine 160 using a dynamometer 150. The test system 100 includes: a dynamometer 150 connected by a shaft 170 with the engine 160, which is the test piece; a throttle actuator 110 and engine control device 120 which control the output of the engine 160; and an inverter 130 and dynamometer control device 140 which control the output of the dynamometer 150. With the test system 100, the durability, fuel economy and exhaust purification performance, etc. of the engine 160 are evaluated by controlling the torque and speed of the dynamometer 150 using the dynamometer control device 140, while controlling the throttle aperture of the engine 160 using the engine control device 120. With the test system 100, a characteristic of the engine 160, especially the moment of inertia of the engine 160, may be measured prior to performing testing to evaluate the above such performance, and this may be used as a control parameter for torque control and speed control in the dynamometer control device 140.
For example, with the method shown in Patent Document 1, the output torque of the dynamometer 150 is vibration controlled while controlling the revolution speed of the engine 160 to be almost constant, and during this, data of the shaft torque generated at the rotation shaft connecting the engine 160 and dynamometer 150 and the revolution speed of the dynamometer 150 are recorded at fixed times, further, a transfer function is estimated that defines the shaft torque as input and revolution speed of the dynamometer 150 as output from this data, and the moment of inertia of the engine 160 is measured using this transfer function.
Although there is an advantage in that the above such estimation method for the moment of inertia is easy, since it is not taking account of the loss due to rotational friction in the engine 160, the estimation precision for the moment of inertia is not high. With the method shown in Patent Document 2, the rotational friction C which is substantially proportional to the revolution speed is measured in advance, and in a state blocking the fuel influx of the engine 160 and fully opening the throttle for blocking the fuel reducing the intake air resistance of the engine 160, it accelerates or decelerates by a fixed acceleration a using the dynamometer 150, the shaft torque T generated at the rotation shaft at this time is measured, and the moment of inertia J is measured using this in an equation of motion (T=J·α+C).
However, the loss due to rotational friction may also depend on the history of variation in revolution speed, not only the steady-state value for the revolution speed of the engine 160. Whereas, with the measurement method of Patent Document 2, since the history for the change in revolution speed is not being taken into consideration, it is not possible to estimate the moment of inertia with good precision.
With the invention described in Patent Document 3, the speed and shaft torque of the dynamometer when randomly exciting the torque of the dynamometer are actually measured, the frequency response HR at the frequency co is calculated using this, and the absolute value of the difference between this actually measured frequency response HR and the model board diagram data HM obtained under a predetermined model parameter PM is integrated over a predetermined frequency band, thereby calculating a performance function. With the invention of Patent Document 3, the model parameter PM such that causes the performance function to converge is obtained by using non-linear programming, and the moment of inertia is measured using this.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2006-300683    Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2003-121307    Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2008-203051